Clean Install

Sometimes the best answer to persistent problems with your Mac is to reinstall the operating system. Of course, to do this, you must have a copy of the System installation disks for your current operating system. This has become increasingly complex with all of the many updates and revisions that have been made in System 7.5. In some cases, the only way to reinstall the system might be to install an old system from a CD-ROM or from the original floppy disks that were shipped with your computer, then install several successive system updates. This inconvenience might, in itself, be sufficient reason to buy a copy of the new System 7.6 on CD.

If you are having a serious problem with your system, it is often wiser to perform a Clean Install of your operating system. A clean install packs away your old operating system (with all of its Control Panels, Extensions, and Preferences) and creates a brand new System Folder that contains only pristine Apple software. Although, this creates more work for you than a standard system install  since all of your custom Extensions, Control Panels, and settings will be lost and must be added back into your new System Folder  it is sometimes the only way to correct accumulated corruptions.

Before we describe the process let's explain one important concept: The new System that you are installing must be on a CD-ROM or floppy disks or some other drive that is capable of acting as a startup disk for your computer. The installer cannot be on your hard drive, because you would be asking your computer to change the system that it is currently running.

To force your computer to ignore the System on the internal hard drive and boot from another System, it may be necessary to do some keyboard gymnastics during the startup process. The key combination is: [Command + Option + Shift + Delete]  while also hitting the Power button on your computer! This requires at least 3 hands! It can be done by holding the [Command + Option + Shift] keys with one hand, hitting the Power button with the other, then quickly hitting the Delete key when the startup chime sounds.

Once the computer is booted with the external System (you can tell because the disk that holds this new System will appear at the upper right of your desktop where your hard drive icon usually is), you should do some disk maintenence before installing the new System. First run the Disk First Aid program (included with the Installer) to check the integrity of your hard drive. Then run Apple HD SC Setup and update your disk driver (this is absolutely essential if you are upgrading your System).

System 7.5

In System 7.5 (all versions) you can use a hidden feature of the Installer to do a Clean Install. Once the Installer is open, before hitting that big INSTALL button, hold down Command + Shift + K (K is for clean, get it?)  then hit the INSTALL button.

A new window will appear asking if you want to the "Install New Sytem Folder" select this and hit OK. This will then give you the "Clean Install" button in the Installer.

Pre-System 7.5

On Systems older than 7.5, Apple did not create any way to perform a clean install using the Installer utility. Instead, it is necessary for you to disable your current system before running the installer. This is, of course, impossible  the Mac OS will not let you delete the System that is currently running the machine. To get around this protection, it is necessary to reboot your machine from a different disk drive. Then you can open the System folder on your hard drive and trash the System itself and the Finder. Then rename your System Folder to something like "Old System Folder" or "Previous System Folder". Now you can launch the Installer program, it will not detect an active System folder on your machine, so it will create a new, clean one.

Using the Installer (all systems)

The Installer has two options, you can choose either Easy Install or Custom Install. You can use the Custom option to limit some of the extra junk that is thrown into your System folder, if you know that you would just be deleting it anyway  but this is for advanced users. Be careful, you could easily mess up your System by choosing not to install some essential components.

Once you hit that big Install button in the lower right, you just have to sit back and watch the process (or feed it disks if you are installing from floppies).

Restoring your System (all systems)

Once the clean install is completed, the hard work really begins. You will have to reset all of your custom Control Panels settings and many of the Preferences from within your favorite applications. You will also have to go through your "Old System Folder" item by item to identify things that you need to have in the new System folder, like third-party Extensions. But instead of just dragging them into the new System folder, you should re-install all third-party Extensions, Control Panels and Fonts from the master disks. It would seem to be easier just dragging them over but that defeats the purpose of the Clean Install  one of these items might be corrupted and actually be the cause of your System problems. Another caution: Do not move Preferences files from the old System to the new System Folder  this is another way to re-introduce corrupted files and Preferences can always be regenerated when you customize your settings in a program.